Field of Invention
The present invention relates to a clock and data recovery circuit with bidirectional frequency detection, in which two types of frequency detection are combined.
Description of Related Art
Clock and data recovery (CDR) is a critical task in all serial communication systems. The main objective of the CDR is to recover the data from the serial input bit stream in an error-free, power and cost-efficient manner. Due to the communication technology progresses, lots of transmission standards are developed such as the universal serial bus (USB), thunderbolt, high-definition multimedia interface (HDMI), serial advanced technology attachment (SATA) and so on. In some display application, the transmission speed varies by resolution, refresh rate, or operating mode. In order to recover the transmitted data for numerous communication standards and transmission speed without external reference clock in the receiver end, a wide range frequency detector and a wide band voltage-controlled oscillator (VCO) are indispensable in such development. However, in some wide-range frequency detectors, it may not precisely trace the frequency of the serial input bit stream; and on the other hand, a precise frequency detector may not have wide frequency range. Therefore, it is an issue in the art that how to provide a precise and wide-range CDR circuit.